The present invention relates to a pressure vessel for use in hydrogen technology and involving particularly the storage of gases having resulted from or accompanying certain reactions as they occur in energy storage systems using exothermic and endothermic reactions and hydride technology generally.
Hydrogen storage vessels are known which are particularly provided for receiving certain metals and compounds of such metals as they are used for the purpose of storage of hydrogen by means of reaction products. These storage vessels are usually of tubular construction. In operation these tubes are situated within the flow field of a heat exchange medium; alternatively, a heat exchange medium passes through a conduit system which is contained in the interior of the vessel referred to above. As a consequence of these operations, reactions occur corresponding to loading or unloading.
The known devices and vessels are disadvantaged by the fact that considerable volumn portions are inherently rather far from the outer wall of the vessel or from the internal heat exchange tube system so that the resulting absorption and desorption is not sufficiently effective to produce the desired intense cooling or heating as the case may be. These disadvantages have been avoided by choosing a diameter for the tubular vessel which is below 30 millimeters. As a consequence, a rather large area becomes available for heat exchange purposes; in other words, the surface to volumn ratio is improved and loading and unloading times are correspondingly improved. However, making vessels of such a small and smaller diameter is rather expensive. This becomes particularly noticable if tubular containers of this type are bunched or bundled, because in addition to the manufacture of a large plurality of relatively small vessels, one needs a rather complicated and expensive manifold and gas collecting system.
Another basic disadvantage inherent in the known system, results from the particular geometry involved and here with regard to the arrangements of the individual vessels. In other words, the particular heat transfer geometry of these systems is poor in general, which becomes particularly noticable during the individual loading and unloading processes. Generally speaking, metal powder is a poor heat conductor. Metal powder portions located directly at heat exchange surfaces are, of course, in relative good heat exchange relation therewith. However, metal powder disposed more in the interior of the vessel operate with significantly reduced efficiency as far as thermo conduction and interaction is concerned. Thus, loading and unloading of these volumn portions run on a considerable enlarged scale. For this reason, it has been a part of the state of the art of hydride stores in general to mix the storage and reactant metal powder with additives that enhance thermo conductivity. By way of example, the particular reacting metal powder was mixed with aluminum powder, for example, by 5 to 10 percent. Since a matrix is formed, the effect is indeed significant to some extent. However, a sizable portion in volumne is lost as far as active material is concerned. Moreover, it was observed that the powder may separate so that locally, again, poor thermo conduction conditions prevail.
Another infavorable aspect of the known hydride storage vessels, particularly in the case of a tubular configuation of the individual vessel portions is to be seen in that the possibility cannot be excluded that the metal powder in the interior dislodges in parts and local variations in densities occur. In particular, there may be portions in which the powder is present in relative dense configuration, while in other portions of the vessel there are cavities. In view of a contemplated employment in the field of motor vehicles one has to consider shaking and shocks which will detrimentally influence the many loading and unloading processes. It may occur, for example, that the powder filling forms gaps and separates temporarily from the interior surface of the tubular vessel. Accordingly, the heat transfer between powder and the particular wall is drastically reduced. Moreover, unwanted local compressions may result in bulging of the vessel even up to rupture which, of course, is a danger that may cause accidents. See here, for example, Phillips research supplement 1976 Volume 1 Page 26, and here particularly FIG. 2.7.
German patent application No. 2,558,690 proposes an improved heat exchanger and container having a circular cross section and tapering in steps or continuously in the direction of gas flow, the gas flow being either subjected to a circulation process of energy of a transverse flow. It must be expected that the resulting interaction is matched to the thermocharacteristic of the process. However, it was found that this approach is not only very expensive, but again, the available volume and enclosed space is insufficiently utilized.
Certain containers have been constructed with a view on equalization of the hydrogen discharge flow and particularly for use in high temperature storage facilities using waste heat or heat from discharged exhaust gas, having a temperature between 300 and 700 degrees centigrade. These constructions include tubular individual containers which are in heat exchange relation with exhaust gases flowing transversely to the axis of the tubes, whereby in addition a cascading arrangement is provided for. This particular approach intends to provide a locally limited but highly effective and concentrated heat transfer into the system. However, the a symmetry of the heat flow results in thermally induced tensions within the solid parts of the system leading in turn to local deformation and ultimately distruction of container facility.
It is furthermore known, that the storage masses of the type used in hydride technology, can be divided or atomized by means of hydrogen with a particle size below 1 micrometer. If one uses such a material, the danger results that upon extraction of hydrogen, some of the material is carried along and may interfer with the function of other parts, such as the engine of the vehicle of which this hydride storage is a part. In order to eliminate this danger one has tried to use sintered metal filters. This approach, however, offers the disadvantage that powdery material sooner or later clogs the filter and interfers and finally blocks the flow of gas.